Current WRA2 Dragster Speed & Distance Record Holder
Joined: Wed Jul 16, 2008 7:19 am
One thing we have found is that for larger volume water rocket cars ... you dont necessarily want the water to be expelled as fast as possible and get as much thrust as you can in the first second or so of the launch.
The water rocket cars arent fighting gravity directly like the water rockets and carrying additional water is not such a big penalty. Also getting the car rolling and having a long thrust period is better for stability than a short higher powered one.
For those that have been following our progress you will know we have had stability and thrust steering issues with our 6.75L water rocket car. One of the ways we have tackled solving this problem is by controlling the thrust by using a reduced diamter nozzle.
We use the gardena 9mm nozzle for our rocket cars and launcher system and have been trying for a while to get a reduced diameter nozzle working. Some of our failures are here
After George from Air command posted a video showing how to use other bottle caps to make a longer threaded nozzle cap, then our solution of using disc inserts in the bottle cap worked as there was plenty of thread left to secure the bottle cap to the bottle. Thanks George.
There is a writeup here of how to make the reduced nozzle disc and longer threaded nozzle cap.
and short video here
Georges excellent video is available here
Then we gave the new nozzle a good test today on a vertical test stand (aka strapped to a tree). Tested it at 80 psi and 140psi with reduced nozzle disc in and out.
Results + writeup are here
Video is here
With the 6mm reduced diameter disc fitted it took 2.3 times longer to expel the water .. giving us a longer thrust phase with lower magnitude thrust .. just what we are after.
This may come in useful for others having stability issues with water rocket cars and is very easy to make
Hornsby Heights Water Rocket Space Agency